Transmitters, receivers and methods of transmitting and receiving

ABSTRACT

The receiver comprises a demodulator configured to detect a signal representing the OFDM symbols and to generate a sampled digital version of the OFDM symbols in the time domain. A Fourier transform processor is configured to receive the time domain digital version of the OFDM symbols and to form a frequency domain version of the OFDM symbols, from which the pilot symbol bearing sub-carriers and the data symbol bearing sub-carriers can be recovered. A detector is configured to recover the data symbols from the data bearing sub-carriers of the OFDM symbols and to recover the pilot symbols from the pilot bearing sub-carriers of the OFDM symbols in accordance with the continuous pilot symbol pattern. The continuous pilot symbols are present at the same sub-carrier locations in first OFDM symbols and as second OFDM symbols. A transmitter is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to United Kingdom ApplicationNumber 1304531.5 filed 13 Mar. 2013 and European Patent OfficeApplication Number 13170706.9 filed 5 Jun. 2013, the contents of whichare incorporated herein by reference in their entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to transmitters, receivers and methods oftransmitting and receiving in an OFDM communications system.

BACKGROUND OF THE DISCLOSURE

There are many examples of radio communications systems in which data iscommunicated using Orthogonal Frequency Division Multiplexing (OFDM).Systems which have been arranged to operate in accordance with DigitalVideo Broadcasting (DVB) standards for example, utilise OFDM. OFDM canbe generally described as providing K narrow band sub-carriers (where Kis an integer) which are modulated in parallel, each sub-carriercommunicating a modulated data symbol such as Quadrature AmplitudeModulated (QAM) symbol or Quadrature Phase-shift Keying (QPSK) symbol.The modulation of the sub-carriers is formed in the frequency domain andtransformed into the time domain for transmission. Since the datasymbols are communicated in parallel on the sub-carriers, the samemodulated symbols may be communicated on each sub-carrier for anextended period, which can be longer than a coherence time of the radiochannel. The sub-carriers are modulated in parallel contemporaneously,so that in combination the modulated carriers form an OFDM symbol. TheOFDM symbol therefore comprises a plurality of sub-carriers each ofwhich has been modulated contemporaneously with different modulationsymbols.

To facilitate detection and recovery of the data at the receiver, theOFDM symbol can include pilot sub-carriers, which communicatedata-symbols known to the receiver. The pilot sub-carriers provide aphase and timing reference, which can be used to estimate an impulseresponse of the channel through which the OFDM symbol has passed andperform tasks such as channel estimation and correction, frequencyoffset estimation etc. These estimations facilitate detection andrecovery of the data symbols at the receiver. In some examples, the OFDMsymbols include both Continuous Pilot (CP) carriers which remain at thesame relative frequency position in the OFDM symbol and Scattered Pilots(SP). The SPs change their relative position in the OFDM symbol betweensuccessive symbols, providing a facility for estimating the impulseresponse of the channel more accurately with reduced redundancy.However, the location of the pilots is required to be known at thereceiver so the receiver can extract the pilot symbols from the correctlocations across the OFDM sub-carriers.

The development of communications system which utilise OFDM symbols tocommunicate data can represent a significant and complex task. Inparticular, the optimisation of communications parameters particular inrespect of frequency planning and network deployment can present asignificant technical problem requiring considerable effort to identifythe communications parameters which are suitable for a communicationssystem which utilises OFDM. As will be appreciated much work has beenperformed to optimise the parameters of DVB standards and in particularDVB T2.

SUMMARY OF THE DISCLOSURE

A receiver recovers data from Orthogonal Frequency Division Multiplexed(OFDM) symbols, the OFDM symbols including a plurality of sub-carriersignals. Some of the sub-carrier signals carrying data symbols and someof the sub-carrier signals carrying pilot symbols, the pilot symbolscomprising scattered pilots symbols and continuous pilot symbols. Thecontinuous pilot symbols are distributed across the sub-carrier signalsin accordance with a continuous pilot symbol pattern and the scatteredpilot symbols are distributed across the sub-carrier signals inaccordance with a scattered pilot signal pattern. The receiver comprisesa demodulator configured to detect a signal representing the OFDMsymbols and to generate a sampled digital version of the OFDM symbols inthe time domain. A Fourier transform processor is configured to receivethe time domain digital version of the OFDM symbols and to form afrequency domain version of the OFDM symbols, from which the pilotsymbol bearing sub-carriers and the data symbol bearing sub-carriers canbe recovered. A detector is configured to recover the data symbols fromthe data bearing sub-carrier signals of the OFDM symbols and to recoverthe pilot symbols from the pilot bearing sub-carrier signals of the OFDMsymbols in accordance with the scattered pilot symbol pattern and thecontinuous pilot symbol pattern. The scattered pilot symbol pattern isone of a plurality of scattered pilot symbol patterns and the continuouspilot pattern is independent of the scattered pilot symbol pattern. Thedetector comprises a memory configured to store a master continuouspilot pattern and a processor configured to detect the number ofsub-carrier signals in the plurality of sub-carrier signals and toderive the continuous pilot pattern from a master pilot pattern based onthe number of sub-carrier signals.

The provision of continuous pilot patterns that are independent ofscattered pilot patterns means that fewer continuous pilot patterns haveto be stored in memory when there is a plurality of scattered pilotpatterns. Furthermore, the ability to derive continuous pilot patternsfrom a master pilot pattern dependent on the number of sub-carriers mayallow fewer continuous plot patterns to be stored in memory when thenumber of sub-carriers varies from symbol to symbol.

In some examples the number of sub-carrier signals in the plurality ofsub-carrier signals is one of a set of sub-carrier signal numbers andthe master pilot symbol pattern is the pilot symbol pattern for thecontinuous pilot symbols for OFDM symbols which include the highestnumber of sub-carrier signals from the set of sub-carrier signalnumbers.

The provision of a master pilot pattern which is for the highest ordersub-carrier mode means that the pilot sub-carrier patterns for modeswith fewer subcarriers can be derived without storing separate pilotpatterns. This therefore may allow a single pilot pattern to be storedthat covers all possible sub-carrier numbers, thus saving memoryanywhere a continuous pilot pattern is required to be stored for eachmode.

In some examples the set of sub-carrier numbers includes approximately 8k, 16 k, and 32 k sub-carriers, the master pilot pattern being providedfor the 32 k sub-carriers, and the continuous pilot pattern for the 8 kand 16 k sub-carriers being derived from the 32 k sub-carrier continuouspilot pattern.

Various further aspects and features of the present technique aredefined in the appended claims and include a transmitter fortransmitting OFDM symbols, a method for transmitting OFDM symbols and amethod for receiving OFDM symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be now be described by way ofexample only with reference to the accompanying drawings where likeparts are provided with corresponding reference numerals:

FIG. 1 provides a schematic diagram of an example OFDM transmitter;

FIG. 2 provides an example OFDM super frame;

FIG. 3 provides a schematic diagram of an example OFDM receiver;

FIG. 4 provides a diagram of part of an example OFDM frame;

FIG. 5 provides a graph illustrating the distribution of continuouspilot locations in a DVB-T2 system that do not coincide with scatteredpilot positions.

FIG. 6 provides a table of continuous pilot symbol sub-carrier locationsfor an 8 k mode in accordance with an example of the present disclosure;

FIG. 7 provides an illustration of continuous pilot symbol sub-carrierlocations for an 8 k mode in accordance with an example of the presentdisclosure;

FIG. 8 provides a histogram of the spacing of continuous pilot symbolsub-carrier locations for an 8 k mode in accordance with an example ofthe present disclosure;

FIG. 9 provides a histogram of dither applied to the continuous pilotsymbol sub-carrier locations in accordance with an example of thepresent disclosure;

FIG. 10 provides a table of continuous pilot symbol sub-carrierlocations for a 16 k mode in accordance with an example of the presentdisclosure;

FIG. 11 provides an illustration of continuous pilot symbol sub-carrierlocations for a 16 k mode in accordance with an example of the presentdisclosure;

FIG. 12 provides a histogram of the spacing of continuous pilot symbolsub-carrier locations for a 16 k mode in accordance with an example ofthe present disclosure;

FIG. 13 provides a table of continuous pilot symbol sub-carrierlocations for a 32 k mode in accordance with an example of the presentdisclosure;

FIG. 14 provides an illustration of continuous pilot symbol sub-carrierlocations for a 32 k mode in accordance with an example of the presentdisclosure;

FIG. 15 provides a histogram of the spacing of continuous pilot symbolsub-carrier locations for a 32 k mode in accordance with an example ofthe present disclosure;

FIG. 16 provides a flow diagram of the operation of a transmitter inaccordance with an example of the present disclosure; and

FIG. 17 provides a flow diagram of the operation of a receiver inaccordance with an example of the present disclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 provides an example block diagram of an OFDM transmitter whichmay be used for example to transmit video images and audio signals inaccordance with the proposed ATSC 3 standard or DVB-T, DVB-H, DVB-T2 orDVB-C2 standards. In FIG. 1 a program source generates data to betransmitted by the OFDM transmitter. A video coder 2, and audio coder 4and a data coder 6 generate video, audio and other data to betransmitted which are fed to a program multiplexer 10. The output of theprogram multiplexer 10 forms a multiplexed stream with other informationrequired to communicate the video, audio and other data. The multiplexer10 provides a stream on a connecting channel 12. There may be many suchmultiplexed streams which are fed into different branches A, B etc. Forsimplicity, only branch A will be described.

As shown in FIG. 1, an OFDM transmitter 20 receives the stream at amultiplexer adaptation and energy dispersal block 22. The multiplexeradaptation and energy dispersal block 22 randomises the data and feedsthe appropriate data to a forward error correction encoder 24 whichperforms error correction encoding of the stream. A bit interleaver 26is provided to interleave the encoded data bits which for the example ina DVB-T2 system is the LDCP/BCH encoder output. The output from the bitinterleaver 26 is fed to a bit into constellation mapper 28, which mapsgroups of bits onto a constellation point of a modulation scheme, whichis to be used for conveying the encoded data bits. The outputs from thebit into constellation mapper 28 are constellation point labels thatrepresent real and imaginary components. The constellation point labelsrepresent data symbols formed from two or more bits depending on themodulation scheme used. These can be referred to as data cells. Thesedata cells are passed through a time-interleaver 30 whose effect is tointerleave data cells resulting from multiple LDPC code words.

The data cells are received by a frame builder 32, with data cellsproduced by branch B etc. in FIG. 1, via other channels 31. The framebuilder 32 then forms many data cells into sequences to be conveyed onOFDM symbols, where an OFDM symbol comprises a number of data cells,each data cell being mapped onto one of a plurality of sub-carriers. Thenumber of sub-carriers will depend on the mode of operation of thesystem, which may include one or more of 8 k, 16 k or 32 k, each ofwhich provides a different number of sub-carriers and therefore fastFourier transform (FFT) sizes.

The sequence of data cells to be carried in each OFDM symbol is thenpassed to the symbol interleaver 33. The OFDM symbol is then generatedby an OFDM symbol builder block 37 which introduces pilot andsynchronising signals generated by and fed from a pilot and embeddedsignal former 36 according to pilot symbol pattern(s). An OFDM modulator38 then forms the OFDM symbol in the time domain which is fed to a guardinsertion processor 40 for generating a guard interval between symbols,and then to a digital to analogue convertor 42 and finally to an RFamplifier within an RF front end 44 for eventual broadcast by the COFDMtransmitter from an antenna 46.

Frame Format

For the system of FIG. 1, the number of sub-carriers per OFDM symbol canvary depending upon the number of pilot and other reserved carriers. Anexample illustration of a “super frame” is shown in FIG. 2.

For example, in DVB-T2, unlike in DVB-T, the number of sub-carriers forcarrying data is not fixed. Broadcasters can select one of the operatingmodes from 1 k, 2 k, 4 k, 8 k, 16 k, 32 k each providing a range ofsub-carriers for data per OFDM symbol, the maximum available for each ofthese modes being 1024, 2048, 4096, 8192, 16384, 32768 respectively. InDVB-T2 a physical layer frame is composed of many OFDM symbols.Typically the frame starts with a preamble or P1 symbol as shown in FIG.2, which provides signalling information relating to the configurationof the DVB-T2 deployment, including an indication of the mode. The P1symbol is followed by one or more P2 OFDM symbols 64, which are thenfollowed by a number of payload carrying OFDM symbols 66. The end of thephysical layer frame is marked by a frame closing symbols (FCS) 68. Foreach operating mode, the number of sub-carriers may be different foreach type of symbol. Furthermore, the number of sub-carriers may varyfor each according to whether bandwidth extension is selected, whethertone reservation is enabled and according to which pilot sub-carrierpattern has been selected.

Receiver

FIG. 3 provides an example illustration of an OFDM receiver which may beused to receive signals transmitted from the transmitter illustrated inFIG. 1. As shown in FIG. 3, an OFDM signal is received by an antenna 100and detected by a tuner 102 and converted into digital form by ananalogue-to-digital converter 104. A guard interval removal processor106 removes the guard interval from a received OFDM symbol, before thepayload data and pilot data is recovered from the OFDM symbol using aFast Fourier Transform (FFT) processor 108 in combination with a channelestimator and corrector 110, an embedded-signalling decoding unit 111and pilot symbol pattern(s). The demodulated data is recovered from ade-mapper 112 and fed to a symbol de-interleaver 114, which operates toeffect a reverse mapping of the received data symbol to re-generate anoutput data stream with the data de-interleaved. Similarly, the bitde-interleaver 116 reverses the bit interleaving performed by the bitinterleaver 26. The remaining parts of the OFDM receiver shown in FIG. 3are provided to effect error correction decoding 118 to correct errorsand recover an estimate of the source data.

Embodiments of the present technique provide a communication systemwhich utilises OFDM to transmit data and reuses much of the systemdesign and configuration parameters which have been adopted for theDVB-T2 standard. However the communication system is adapted to transmitOFDM symbols within channels of 6 MHz rather than the 8 MHz which isused for the DVB T2 standard and utilise 8 k, 16 k and 32 k modes.Accordingly, the present disclosure presents an adaptation of theparameters for an OFDM system for 6 MHz but rationalising where possiblethe parameters that were developed for the DVB T2 standard to simplifyarchitecture and implementation of a communications system.

In some embodiments the 8 k mode is an operating mode in which thenumber of active or useful subcarriers lies between 4097 and 8192, the16 k mode is an operating mode in which the number of active or usefulsubcarriers lies between 8192 and 16384, and the 32 k mode is anoperating mode in which the number of active useful subcarriers liesbetween 16385 and 32768.

In some embodiments, when referring to 6 MHz bandwidth herein, inpractice the useful bandwidth is approximately 5.71 MHz or 5.70 MHzallowing for small guard bands and/or depending on the precise number ofactive sub-carriers used.

Pilot Symbols

In addition to signalling data and a payload data, OFDM frames and thecells they include may also comprise pilot symbols which have beeninserted at the transmitter. These pilot symbols may for instance havebeen generated by the pilot and embedded signal former 36 and insertedby the symbol builder 37. Pilot symbols are transmitted with a knownamplitude and phase and the sub-carriers upon which they are transmittedmay be termed pilot sub-carriers. Pilot symbols may be required for arange of different purposes at the receiver, for example, channelestimation, synchronisation, coarse frequency offset estimation and finefrequency offset estimation. Due to the a priori knowledge of the pilotsymbols' amplitude and phase, the channel impulse response may beestimated based on the received pilot symbols, with the estimatedchannel then being used for purposes such as equalisation.

In order for the receiver to receive the pilot symbols and differentiatethe pilots signals from other signalling symbols and data symbols, thepilot symbols may be distributed across the subcarriers and symbols ofan OFDM frame according to a sub-carrier pilot symbol pattern.Consequently, if the receiver has knowledge of pilot symbol pattern andis synchronised with the OFDM frame, it will be able to extract thereceived pilot symbols from the appropriate locations or sub-carriers inthe OFDM symbols and frame.

The distribution of pilots with respect to OFDM sub-carriers may fallinto two categories: continuous pilots and scattered pilots. Continuouspilots are formed from pilot symbols whose location relative to thesub-carriers does not change from symbol to symbol with the result thatthey are transmitted on a same sub-carrier each time. Scattered pilotsbroadly describe pilot symbols whose location changes from symbol tosymbol, possibly according to some repeating pattern.

FIG. 4 illustrates a series of OFDM symbols where the circles representOFDM cells and shaded circles represent pilot symbols. In FIG. 4 thehorizontal direction represents frequency or the sub-carrier number, andthe vertical direction represents time or the symbol number. Continuouspilot symbols 120 are located on the same subcarrier (CP) each timewhereas scattered pilots 122 are located on different sub-carriers fromsymbol to symbol. The repetition of the scattered pilots can berepresented by variables Dx and Dy. Dx represents a separation betweenscattered pilots in the frequency domain from one OFDM symbol toanother, so that the scattered pilot symbols on a first OFDM symbol isdisplaced by a number of sub-carriers equal to Dx in the frequencydomain on a subcarrier in the next OFDM symbol. Dy represents aparameter indicating a number of OFDM symbols before the same subcarrieris used again to carry a pilot symbol on the next occasion. Forinstance, in FIG. 4 the location of the scattered pilots symbols may berepresented by Dy=8, and Dx=10. Scattered pilots are an efficient way ofproviding pilot symbols because channel estimates for sub-carriers andsymbols in between scattered pilot symbols can be estimated byinterpolation in both time and frequency from the known pilot symbols orchannel estimates. Consequently, pilot symbols may not be required to bepresent on all sub carriers in order to obtain channel estimates foreach sub-carrier and cell within an OFDM frame.

Pilot symbols occupy sub-carriers and cells which may otherwise becarrying data, therefore pilot symbols adversely affect the capacity ofa system and it may be advantageous to minimise the number of pilotsymbols. Consequently, a well-designed pilot pattern that enableschannel estimates etc. to be obtained across the entire OFDM framewhilst using a small number of pilot symbols is desirable.

The scattered pilot pattern chosen for an OFDM signal may be dependentupon a number of factors, such as the rate of channel variation withrespect to time and frequency. For instance, the density of the pilotsmust fulfil the sampling theorem in both time and frequency if accuratechannel estimates are to be obtained i.e. the maximum channel impulsesresponse length determines the pilot symbol repetition in the frequencydirection, and the maximum Doppler frequency of the channels determinesthe pilot symbol repetition in the time domain. In some example OFDMsystems the guard interval is determined by the length of the channelimpulse response and therefore the pilot symbol repetition in thefrequency direction may also be dependent upon the guard intervalduration.

It may be beneficial if the location of continual pilot symbols andscattered pilot symbols do not overlap or coincide so that there is anapproximately constant number of pilot symbols per frame and there areno significant “blind spots”. In OFDM frames where there is large numberof neighbouring cells which do not include a pilot symbol, this area maybe referred to as a blind spot. It is generally desirable to avoid suchsituations because they may lead to reduced accuracy channel estimationand interpolation as well as a possible inability to detect andcompensate for coloured noise such as analogue TV or other narrow bandinterference. FIG. 5 provides a graph of continuous pilot locationswhich do not coincide with scattered pilot positions in a DVB-T2 systemand illustrates the aforementioned problems, where blind spots 124 areshown as regions where there is a lack of pilot symbols. Also shown inFIG. 5 are the edges of the frequency band 126 where measurements takenvia pilot symbols on these regions may be subject to increased noise andattenuation and should therefore be avoided if possible.

A measure of the extent which continual pilot symbols and scatteredpilots symbol coincide may be referred to as a utilisation ratio, andcan be calculated using the formula below

${{Utilisation}\mspace{14mu}{Ratio}} = {\frac{{Number}\mspace{14mu}{of}\mspace{14mu}{CPnSP}}{{Total}\mspace{14mu}{Number}\mspace{14mu}{of}\mspace{14mu}{CP}} \times 100\%}$where CPnSP represents the number of continual pilot symbols which donot coincide with scattered pilots sub-carriers during an OFDM frame.Consequently, due to the reasons given above, it may be beneficial totry and maximise the utilisation ratio. There are also a number of otherfactors which may have to be taken into account when determining thescattered pilot and continual pilot patterns, for instance, it may notbe useful to have pilot symbols close to the outer sub-carriers of anOFDM signal because it is likely that these sub-carriers may be withinthe transition band of tuner filters and be subject to extra noise asmentioned above. It may also be beneficial to randomise the location ofpilot symbols to some extent in order to ensure that interference isadequately modelled and reliable channel estimates obtained.Furthermore, due to the dependence of the scattered pilot patterns onfactors such as the guard interval duration and Doppler spread, an OFDMsystem may have a plurality of scattered pilot patterns available touse, each specified by the repetition rates Dx and Dy.

Due to the possible variation of scattered pilot patterns, in order tomaximise the utilisation ratio, minimise blind spots and avoid pilotssymbols being located close to the outer sub-carriers, differentcontinuous pilot patterns may be required for one or more of thescattered pilots patterns. For instance, in DVB-T2 in some modes thereare eight scattered pilot patterns and eight corresponding continuouspilot patterns. In some OFDM systems there may be more than one patternper mode and different patterns across different modes so that in totalthere may be a significant number of pilot patterns.

The pilot signal embedder 36 which embeds the pilot symbols at thetransmitter and the pilot signal extractor 111 which extracts the pilotsymbols at the receiver require knowledge of the pilot patterns.Consequently, it is likely that all the pilot patterns which may be usedin a system will have to be stored in ROM at both the transmitter andthe receiver, thus requiring a significant amount of memory if there aremultiple modes and multiple pilot patterns per mode. This memoryrequirement is particularly relevant to the receiver in a broadcastsystem because there is likely to be a large number of receiverscompared to transmitters and the cost of the receivers is likely to belower than that of the transmitters. Consequently, reducing memoryrequirements will likely be beneficial, especially in the receiver sideof a system.

In addition to memory requirements, utilising a large number ofdifferent scattered and continuous pilot patterns in a system also makesthe system more complex because the transmitter has to select whichpilot pattern is most appropriate for the current channel conditions andsignal properties, and the receiver needs to identify the pilot patternwhich is being used. The receiver may do this via the signallinginformation which specifies the pilot pattern(s) and mode of operation,or the receiver may detect the mode and pilot patterns viacharacteristics of the signal. However, both of these approaches becomemore complex and have larger overheads when more pilot patterns areavailable in a system. Therefore, it would be desirable to reduce thenumber of pilot patterns which are used in a system whilst maximisingthe utilisation ratio, avoiding blinds spots and minimising the numberof pilots near to the outer sub-carriers.

In accordance with an example of the present technique, an OFDM systemwith a 6 MHz bandwidth and 8 k, 16 k, and 32 k modes has a singlecontinuous pilot sub-carrier pattern for each mode, which is suitablefor use with a plurality of different scattered pilot symbol patternswithin each mode. In one example, there is a continuous pilot patternwhich is suitable for use with one or more of the scattered pilotpatterns given in Table 2 the below

TABLE 2 Scattered Pilot Patterns Scattered Pilot Pattern Dx Dy P4, 2 4 2P4, 4 4 4 P8, 2 8 2 P16, 2 16 2 P32, 2 32 2

In an 8 k mode (normal or extended) of an OFDM system that utilises thescattered pilots sequence given in Table 2 above, the distribution ofthe continuous pilots may be given by the table in FIG. 6. The samelocations as given in FIG. 6 are also given by 41, 173, 357, 505, 645,805, 941, 1098, 1225, 1397, 1514, 1669, 1822, 1961, 2119, 2245, 2423,2587, 2709, 2861, 3026, 3189, 3318, 3510, 3683, 3861, 4045, 4163, 4297,4457, 4598, 4769, 4942, 5113, 5289, 5413, 5585, 5755, 5873, 6045, 6207,6379, 6525, 6675, 6862 in terms of sub-carrier locations in the extendedbandwidth mode. For operation in normal 8 k mode the pilot pattern maybe derived by discarding the final sub-carrier location. The location ofthe continuous pilot symbols relative to the sub-carriers given in FIG.6 do not coincide with the location of the scattered pilots given inTable 2 above and therefore the continuous pilot pattern obtains autilisation ratio of 100%. FIG. 7 graphically illustrates the locationof the continuous pilots of FIG. 6 for the extended 8 k mode and showsthat there is a substantially uniform distribution of continuous pilotsacross the subcarriers of the extended 8 k mode without any substantialblind spots. FIG. 8 provides a histogram of the continuous pilot symbolspacing with respect to sub-carriers. The histogram once again showsthat there is a substantially consistent distribution of continuouspilot symbols across the sub-carriers, thus reinforcing the absence ofblind spots. Although the distribution of pilot symbols across thesub-carriers is substantially uniform, their location has beenrandomised to some extent by the introduction of dither. FIG. 9illustrates the dither which has been applied to the placement of thecontinuous pilot symbols in FIG. 6.

In a 16 k mode (normal or extended) of an OFDM system that utilises thescattered pilots sequence given in Table 2 above, the distribution ofthe continuous pilots may be given by the table in FIG. 10. The samelocations as given in FIG. 10 are also given by 82, 243, 346, 517, 714,861, 1010, 1157, 1290, 1429, 1610, 1753, 1881, 2061, 2197, 2301, 2450,2647, 2794, 2899, 3027, 3159, 3338, 3497, 3645, 3793, 3923, 4059, 4239,4409, 4490, 4647, 4847, 5013, 5175, 5277, 5419, 5577, 5723, 5895, 6051,6222, 6378, 6497, 6637, 6818, 7021, 7201, 7366, 7525, 7721, 7895, 8090,8199, 8325, 8449, 8593, 8743, 8915, 9055, 9197, 9367, 9539, 9723, 9885,10058, 10226, 10391, 10578, 10703, 10825, 10959, 11169, 11326, 11510,11629, 11747, 11941, 12089, 12243, 12414, 12598, 12758, 12881, 13050,13195, 13349, 13517, 13725, 13821 in terms of sub-carrier locations inthe extended bandwidth mode. For operation in normal 16 k mode the pilotpattern may be derived by discarding the final two sub-carrierlocations. The location of the continuous pilot symbols relative to thesub-carriers given in FIG. 10 do not coincide with the location of thescattered pilots given in Table 2 above and therefore the continuouspilot pattern obtains a utilisation ratio of 100%. FIG. 11 graphicallyillustrates the location of the continuous pilots of FIG. 10 for theextended 16 k mode and shows that there is a substantially uniformdistribution of continuous pilots across the subcarriers of the extended16 k mode without any substantial blind spots. FIG. 12 provides ahistogram of the continuous pilot symbol spacing with respect tosub-carriers. The histogram once again shows that there is asubstantially consistent distribution of continuous pilot symbols acrossthe sub-carriers, thus reinforcing the absence of blind spots. As forthe 8 k mode, although the distribution of pilot symbols across thesub-carriers is substantially uniform, their location has beenrandomised to some extent by the introduction of dither. The same ditheras applied to the 8 k continuous pilot symbol placement has also beenapplied to the 16 k continuous pilot symbol placement and therefore FIG.9 illustrates the dither which has been applied the placement of thecontinuous pilot symbols in FIG. 10.

In a 32 k mode of an OFDM system that utilises the scattered pilotssequence given in Table 2 above, the distribution of the continuouspilots may for example be given by the table in FIG. 13. The samelocations as given in FIG. 13 are also given by 163, 290, 486, 605, 691,858, 1033, 1187, 1427, 1582, 1721, 1881, 2019, 2217, 2314, 2425, 2579,2709, 2857, 3009, 3219, 3399, 3506, 3621, 3762, 3997, 4122, 4257, 4393,4539, 4601, 4786, 4899, 5095, 5293, 5378, 5587, 5693, 5797, 5937, 6054,6139, 6317, 6501, 6675, 6807, 6994, 7163, 7289, 7467, 7586, 7689, 7845,8011, 8117, 8337, 8477, 8665, 8817, 8893, 8979, 9177, 9293, 9539, 9693,9885, 10026, 10151, 10349, 10471, 10553, 10646, 10837, 10977, 11153,11325, 11445, 11605, 11789, 11939, 12102, 12253, 12443, 12557, 12755,12866, 12993, 13150, 13273, 13445, 13635, 13846, 14041, 14225, 14402,14571, 14731, 14917, 15050, 15209, 15442, 15622, 15790, 15953, 16179,16239, 16397, 16533, 16650, 16750, 16897, 17045, 17186, 17351, 17485,17637, 17829, 17939, 18109, 18246, 18393, 18566, 18733, 18901, 19077,19253, 19445, 19589, 19769, 19989, 20115, 20275, 20451, 20675, 20781,20989, 21155, 21279, 21405, 21537, 21650, 21789, 21917, 22133, 22338,22489, 22651, 22823, 23019, 23205, 23258, 23361, 23493, 23685, 23881,24007, 24178, 24317, 24486, 24689, 24827, 25061, 25195, 25331, 25515,25649, 25761, 25894, 26099, 26246, 26390, 26569, 26698, 26910, 27033,27241, 27449, 27511, 27642, 27801 in terms of sub-carrier locations inthe extended bandwidth mode. For operation in normal 32 k mode the pilotpattern may be derived by discarding the final four sub-carrierlocations. The location of the continuous pilot symbols relative to thesub-carriers given in FIG. 14 do not coincide with the location of thescattered pilots given in Table 2 above and therefore the continuouspilot pattern obtains a utilisation ratio of 100%. FIG. 14 graphicallyillustrates the location of the continuous pilots of FIG. 13 for theextended 32 k mode and shows that there is a substantially uniformdistribution of continuous pilots across the subcarriers of the extended8 k mode without any substantial blind spots. FIG. 15 provides ahistogram of the continuous pilot symbol spacing with respect tosub-carriers. The histogram once again shows that there is asubstantially consistent distribution of continuous pilot symbols acrossthe sub-carriers, thus reinforcing the absence of blind spots. As forthe 8 k and 16 k modes, although the distribution of pilot symbolsacross the sub-carriers is substantially uniform, their location hasbeen randomised to some extent by the introduction of dither. The samedither as applied to the 8 k and 16 k continuous pilot symbol placementhas also been applied to the 32 k continuous pilot symbol placement andtherefore FIG. 9 illustrates the dither which has been applied theplacement of the continuous pilot symbols in FIG. 13.

As previously mentioned, the proposed continuous pilot patternsdescribed above may also achieve substantially a 100% utilisation ratio,however, they also achieve a capacity loss which is approximately 0.65%in a system such as a proposed ATSC 3 system as previously described.

The continuous pilot patterns specified above may provide advantagesover existing continuous pilot patterns because only a single continuouspilot pattern is required to operate with all five of the scatteredpilots patterns specified in Table 2. Furthermore, these pilot patternsalso reduce the number of blind spots in comparison to continuous pilotpatterns such as those specified in DVB-T2. Since only one continuouspilot pattern is required to be stored at both the transmitter and thereceiver compared to five if conventional continuous pilot patterns wereused, memory requirements have been reduced by approximately 80%.However, memory for multiple continuous pilot patterns may still berequired when there is more than one mode of operation e.g. 8 k, 16 k,32 k, and both normal and extended modes are available. Consequently, ina system such as a proposed ATSC 3 system where there are three modes,it is likely that three continuous pilot patterns are still required tobe stored.

In accordance with another example of the present technique, thecontinuous pilots patterns illustrated in FIGS. 6, 10, and 13 arerelated such that the continuous pilot patterns of the 8 k and the 16 kmodes are derivable from the 32 k mode continuous pilot symbol pattern.This therefore allows a transmitter and a receiver to store only asingle master continuous pilot pattern for the highest order mode thenderive the continuous pilot patterns for lower order modes when they arerequired.

For instance, at the transmitter the pilot and embedded signal former 36may comprise a processor which is operable to detect or receive datawhich conveys the operating mode of the OFDM system and then derive theappropriate continuous pilot pattern from a master pilot pattern basedon the number of sub-carriers, where the master pilot pattern is storedin a memory at the pilot and embedded signal former 36. In the case ofthe continuous pilot patterns discussed above, the master continuouspilot pattern would be the 32 k pilot pattern and the 16 k continuouspilot pattern and the 8 k continuous pilot pattern would be derived fromthe 32 k pilot pattern by the processor according to the followingequations below where the master pilot pattern is given by the followingsub-carrier locations for the extended bandwidth mode 163, 290, 486,605, 691, 858, 1033, 1187, 1427, 1582, 1721, 1881, 2019, 2217, 2314,2425, 2579, 2709, 2857, 3009, 3219, 3399, 3506, 3621, 3762, 3997, 4122,4257, 4393, 4539, 4601, 4786, 4899, 5095, 5293, 5378, 5587, 5693, 5797,5937, 6054, 6139, 6317, 6501, 6675, 6807, 6994, 7163, 7289, 7467, 7586,7689, 7845, 8011, 8117, 8337, 8477, 8665, 8817, 8893, 8979, 9177, 9293,9539, 9693, 9885, 10026, 10151, 10349, 10471, 10553, 10646, 10837,10977, 11153, 11325, 11445, 11605, 11789, 11939, 12102, 12253, 12443,12557, 12755, 12866, 12993, 13150, 13273, 13445, 13635, 13846, 14041,14225, 14402, 14571, 14731, 14917, 15050, 15209, 15442, 15622, 15790,15953, 16179, 16239, 16397, 16533, 16650, 16750, 16897, 17045, 17186,17351, 17485, 17637, 17829, 17939, 18109, 18246, 18393, 18566, 18733,18901, 19077, 19253, 19445, 19589, 19769, 19989, 20115, 20275, 20451,20675, 20781, 20989, 21155, 21279, 21405, 21537, 21650, 21789, 21917,22133, 22338, 22489, 22651, 22823, 23019, 23205, 23258, 23361, 23493,23685, 23881, 24007, 24178, 24317, 24486, 24689, 24827, 25061, 25195,25331, 25515, 25649, 25761, 25894, 26099, 26246, 26390, 26569, 26698,26910, 27033, 27241, 27449, 27511, 27642, 27801.

In order to derive the 16 k continuous pilot locations from the 32 kpilot positions given in FIG. 13 and above, every other 32 k continuouspilot position is taken, the position divided by two and the resultrounded up. In terms of a computer implementable equation, this is givenbyCP_(—)16K_pos=round(CP_(—)32K_pos(1:2:last_(—)32k_cp_pos)/2).In order to derive the 8 k continuous pilot locations from the 32 kpilot positions given in FIG. 13 every four of the 32 k continuous pilotpositions is taken, the taken position divided by four and the resultrounded up. In terms of a computer implementable equation, this is givenbyCP_(—)8K_pos=round(CP_(—)32K_pos(1:4:last_(—)32k_cp_pos)/4).Using the equations above it is possible that the 8 k, 16 k and 32 kcontinuous pilot patterns may be derived from a single master set andtherefore an OFDM system is effectively able to operate with a singlecontinuous pilot pattern across all modes and all scattered pilotpatterns. This may therefore simplify the operation of an OFDM system interms of memory requirements but also the processing required because itis no longer necessary to switch between independent continuous pilotpatterns which are unrelated.

Although in the preceding paragraphs the derivation of the continuouspilot patterns takes place at the transmitter, a similar process mayalso be performed at the receiver. For instance, the embedded signaldecoding unit 111 may also comprises a processor which is substantiallysimilar the processor described with reference to the pilot and embeddedsignal former 36. The processor would be operable to detect or receivedata which conveys the operating mode of the OFDM system i.e. number ofsub-carriers per OFDM symbol, and then derive the appropriate continuouspilot pattern from a master pilot pattern as previously described.

Due to the computational simplicity of the derivation processesdescribed above, a decrease in ROM memory requirements i.e. the memoryrequired to store the 8 k and 16 k continuous pilot patterns, may beachieved with only a small increase computational complexity. In someexamples in accordance with the present technique, the derivation in thetransmitter and the receiver may be performed by existing computationalelements within the pilot related elements and therefore no additionalcomponents would be required in these cases.

In other examples in accordance with the present technique, thecontinuous pilot patterns for 8 k, 16 k and 32 k modes may be used in anOFDM system, such as an ATSC 3.0 system for example, in order to exploitthe intrinsic advantages of the continuous pilot symbol patterns. Forinstance, the advantages relating to the regular distribution of thepilot locations and the reduction in pilot locations near the outersub-carriers can be achieved by one of the continuous pilot sub-carrierpatterns with the following indices:

41, 173, 357, 505, 645, 805, 941, 1098, 1225, 1397, 1514, 1669, 1822,1961, 2119, 2245, 2423, 2587, 2709, 2861, 3026, 3189, 3318, 3510, 3683,3861, 4045, 4163, 4297, 4457, 4598, 4769, 4942, 5113, 5289, 5413, 5585,5755, 5873, 6045, 6207, 6379, 6525, 6675, (6862) for the 8 k mode;82, 243, 346, 517, 714, 861, 1010, 1157, 1290, 1429, 1610, 1753, 1881,2061, 2197, 2301, 2450, 2647, 2794, 2899, 3027, 3159, 3338, 3497, 3645,3793, 3923, 4059, 4239, 4409, 4490, 4647, 4847, 5013, 5175, 5277, 5419,5577, 5723, 5895, 6051, 6222, 6378, 6497, 6637, 6818, 7021, 7201, 7366,7525, 7721, 7895, 8090, 8199, 8325, 8449, 8593, 8743, 8915, 9055, 9197,9367, 9539, 9723, 9885, 10058, 10226, 10391, 10578, 10703, 10825, 10959,11169, 11326, 11510, 11629, 11747, 11941, 12089, 12243, 12414, 12598,12758, 12881, 13050, 13195, 13349, 13517, (13725, 13821) for the 16 kmode; and163, 290, 486, 605, 691, 858, 1033, 1187, 1427, 1582, 1721, 1881, 2019,2217, 2314, 2425, 2579, 2709, 2857, 3009, 3219, 3399, 3506, 3621, 3762,3997, 4122, 4257, 4393, 4539, 4601, 4786, 4899, 5095, 5293, 5378, 5587,5693, 5797, 5937, 6054, 6139, 6317, 6501, 6675, 6807, 6994, 7163, 7289,7467, 7586, 7689, 7845, 8011, 8117, 8337, 8477, 8665, 8817, 8893, 8979,9177, 9293, 9539, 9693, 9885, 10026, 10151, 10349, 10471, 10553, 10646,10837, 10977, 11153, 11325, 11445, 11605, 11789, 11939, 12102, 12253,12443, 12557, 12755, 12866, 12993, 13150, 13273, 13445,13635, 13846, 14041, 14225, 14402, 14571, 14731, 14917, 15050, 15209,15442, 15622, 15790, 15953, 16179, 16239, 16397, 16533, 16650, 16750,16897, 17045, 17186, 17351, 17485, 17637, 17829, 17939, 18109, 18246,18393, 18566, 18733, 18901, 19077, 19253,19445, 19589, 19769, 19989, 20115, 20275, 20451, 20675, 20781, 20989,21155, 21279, 21405, 21537, 21650, 21789, 21917, 22133, 22338, 22489,22651, 22823, 23019, 23205, 23258, 23361, 23493, 23685, 23881, 24007,24178, 24317, 24486, 24689, 24827, 25061,25195, 25331, 25515, 25649, 25761, 25894, 26099, 26246, 26390, 26569,26698, 26910, 27033, 27241, (27449, 27511, 27642, 27801) for the 32 kmode, where the values in brackets relate to the extended bandwidthmodes.

In some embodiments, in the proposed ATSC3.0 frame structure, OFDMsymbols in different physical layer frames may have different subcarrierspacing. Frequency domain frame synchronization in preamble detection isthus not readily possible. The preamble symbol (as generated by an L1signaling unit) must therefore be detected in the time domain. It isonly after the preamble is decoded and its signaling payload interpretedthat frequency domain processing of the frame can proceed. The newpreamble fulfills all specific requirements:

-   -   Synchronization capabilities;    -   Offset correction capabilities;    -   Robustness of signaling;    -   Protection against interference.

In some embodiments, the same preamble is used for all frame types. Itconsists of a regular 8 k symbol with an extended guard interval GI(fractional length 57/128). This GI is chosen to map to the longestpossible guard interval for a 32 k FFT size, i.e. 57/512). In someembodiments ISI avoidance for all frame types is therefore guaranteed.

In some embodiments, for the standard bandwidth (i.e. 6 MHz), thepreamble symbol allocates 6912 subcarriers and contains 45 frequencyoffset estimation pilots at the same locations as the continual pilotsof a payload symbol. In some embodiments no other pilots are foreseen.The 6867 payload carriers use BPSK modulation for L1 signaling.

In some embodiments, the preamble symbol uses an overlaid time domainpilot signal (SigSeq). This requires good ACF (auto correlationfunction) properties that allow for accurate frame synchronization andchannel impulse response (CIR) estimation. The full-band ChannelTransfer Function estimation at the receiver is accordingly calculatedfrom the CIR.

Summary of Operation

An example flow diagram illustrating the operation of a transmitteraccording to the present technique is shown in FIG. 16, an operation ofa receiver to detect and recover data from a received OFDM symbol isprovided in FIG. 17. The process steps illustrated in FIG. 15 aresummarised as follows:

S1: As a first step to transmitting data using OFDM symbols a dataformatter receives the data for transmission and forms the data intosets of data symbols for each of the OFDM symbols for transmission. Thusthe data symbols are formed into the sets each have a number of datasymbols corresponding to an amount of data which can be carried by anOFDM symbol.

S2: An OFDM symbol builder then receives each of the sets of datasymbols from the data formatter and combines the data symbols with pilotsymbols according to predetermined scattered and continuous pilotpatterns. In accordance with the present technique, the pilot patternsare given by Table 2 for scatted pilots and FIGS. 6, 10, and 13 forcontinuous pilots, where the sub-carrier locations in FIG. 6 and FIG. 10may be derived from the locations given in FIG. 13. The predeterminedpattern sets out the subcarriers of the OFDM symbol which are to carrythe pilot symbols. The remaining subcarriers of the OFDM symbol carrythe data symbols. The OFDM symbols therefore each include a plurality ofsubcarrier symbols, some of the subcarrier symbols carrying data symbolsand some of the subcarrier symbols carrying pilot symbols.

S4: A modulator maps the data symbols and the pilot symbols ontomodulation symbols in accordance with the value of the data symbols andthe pilot symbols. With the modulation symbols each of the subcarriersis then modulated to form the OFDM symbols in the frequency domain.

S6: An inverse Fourier transformer then converts the OFDM symbols in thefrequency domain into the time domain within a bandwidth of thecommunication system which is 6 MHz or approximately 6 MHz.

S8: A guard interval inserter adds a guard interval to each of the timedomain OFDM symbols by copying a part of the OFDM symbols which is auseful part containing data symbols or pilot symbols and appending thecopied part sequentially in the time domain to the OFDM symbols. Thepart which is copied has a length which corresponds to a guard intervalwhich is a predetermined guard interval duration.

S10: A radio frequency transmission unit then modulates a radiofrequency carrier with the time domain OFDM symbols and transmits theOFDM symbols via an antenna of the transmitter.

The operation of a receiver to detect and recover data from the OFDMsymbols transmitted by the method of transmission is presented in FIG.17 which are summarised as follows:

S12: A demodulator receives a signal from an antenna and a radiofrequency down converter and detects a signal representing the OFDMsymbols. The demodulator generates a sampled digital version of the OFDMsymbols in the time domain. A bandwidth of the OFDM symbols in thefrequency domain in accordance with the present technique issubstantially 6 MHz, that is approximately 6 MHz.

S14: A guard interval correlator correlates the set of samplescorresponding to the guard interval of the OFDM symbols to detect atiming of a useful part of the OFDM symbols. A section of the receivedsignal samples corresponding to the guard interval are copied and storedand then correlated with respect to the same received signal samples inorder to detect a correlation peak identifying where the repeated guardintervals are present in the useful part of the OFDM symbols.

S16: A Fourier transform processor then transforms a section of the timedomain samples of the received signal for a useful part of the OFDMsymbols identified by the timing detected by the guard intervalcorrelator into the frequency domain using a Fourier transform. From theOFDM symbols in the frequency domain the pilot symbols can be recoveredfrom the pilot symbol bearing subcarriers and data symbols can berecovered from data bearing subcarriers. In accordance with the presenttechnique, the pilot sub-carrier locations are given by Table 2 forscatted pilots and FIGS. 6, 10, and 13 for continuous pilots, where thesub-carrier locations in FIG. 6 and FIG. 10 may be derived from thelocations given in FIG. 13.

S18: A channel estimation and correction unit estimates an impulseresponse of a channel through which the OFDM symbols have passed fromthe recovered pilot symbols and corrects the received data symbolsbearing subcarriers using the estimated channel impulse response.Typically this is in accordance with the equalisation technique wherethe received signal in the frequency domain is divided by a frequencydomain representation of the channel impulse response.

S20: A de-mapper recovers the data symbols from the data bearingsubcarriers of the OFDM symbols by performing a reverse mapping to thatwhich was performed at the transmitter.

As will be appreciated the transmitter and receiver shown in FIGS. 1 and3 respectively are provided as illustrations only and are not intendedto be limiting. For example, it will be appreciated that the presenttechnique can be applied to a different transmitter and receiverarchitecture.

As mentioned above, embodiments of the present invention findapplication with an ATSC standard such as ATSC 3.0, which areincorporated herein by reference. For example embodiments of the presentinvention may be used in a transmitter or receiver operating inaccordance with hand-held mobile terminals. Services that may beprovided may include voice, messaging, internet browsing, radio, stilland/or moving video images, television services, interactive services,video or near-video on demand and option. The services might operate incombination with one another. In the proposed ATSC3.0 frame structure,which will be explained in more detail below, OFDM symbols in differentphysical layer frames may have different subcarrier spacing. Frequencydomain frame synchronization in (preamble detection) is thus not readilypossible. The preamble symbol (as generated by the L1 signaling unit 15)must therefore be detected in the time domain. It is only after thepreamble is decoded and its signaling payload interpreted that frequencydomain processing of the frame can proceed. The new preamble fulfillsall specific requirements:

-   -   Synchronization capabilities;    -   Offset correction capabilities;    -   Robustness of signaling;    -   Protection against interference.        The same preamble is used for all frame types. As shown in FIG.        14 (showing the time domain characteristics of the preamble        symbol) it consists of a regular 8 k symbol with an extended        guard interval GI (fractional length 57/128). This GI is chosen        to map to the longest possible guard interval for a 32 k FFT        size, i.e. 57/512). ISI avoidance for all frame types is        therefore guaranteed.        For the standard bandwidth (i.e. 6 MHz), the preamble symbol        allocates 6912 subcarriers and contains 45 frequency offset        estimation pilots at the same locations as the continual pilots        of a payload symbol. No other pilots are foreseen. The 6867        payload carriers use BPSK modulation for L1 signaling.        The preamble symbol uses an overlaid time domain pilot signal        (SigSeq). This requires good ACF (auto correlation function)        properties that allow for accurate frame synchronization and        channel impulse response (CIR) estimation. The full-band Channel        Transfer Function estimation at the receiver is accordingly        calculated from the CIR.

The SigSeq consists of one of two possible constant amplitude zeroautocorrelation (CAZAC) sequences in order to allow power efficient EWS.CAZAC sequences have been chosen due to their excellent correlationproperties in time and frequency domain as well as their band-limitedspectrum behavior. Due to the fixed size of the guard interval thesearch for preamble can be limited to Ng samples (i.e. the number ofsamples of the guard interval).

Embodiments of the disclosure provide a receiver configured torecovering data from Orthogonal Frequency Division Multiplexed (OFDM)symbols,

wherein the OFDM symbols include a plurality of sub-carrier signals,some of the sub-carrier signals carrying data symbols and some of thesub-carrier signals carrying pilot symbols, the pilot symbols comprisingcontinuous pilots symbols, the continuous pilot symbols beingdistributed with irregular spacing across the sub-carrier signals inaccordance with a continuous pilot symbol pattern, the receivercomprising:

a demodulator configured to detect a signal representing the OFDMsymbols, and to generate a sampled digital version of the OFDM symbolsin the time domain,

a Fourier transform processor configured to receive the time domaindigital version of the OFDM symbols and to form a frequency domainversion of the OFDM symbols, from which the continuous pilot symbolbearing sub-carriers and the data symbol bearing sub-carriers can berecovered, and

a detector configured to recover the data symbols from the data bearingsub-carrier signals of the OFDM symbols and to recover the pilot symbolsfrom the pilot bearing sub-carrier signals of the OFDM symbols inaccordance with the continuous pilot symbol pattern, wherein thecontinuous pilot pattern is independent of the scattered pilot symbolpattern, and the detector comprises a memory configured to store amaster continuous pilot pattern and a processor configured to detect thenumber of sub-carrier signals in the plurality of sub-carrier signalsand to derive the continuous pilot pattern from a master pilot patternbased on the number of sub-carrier signals.

Embodiments of the disclosure provide a transmitter for transmittingOrthogonal Frequency Division Multiplexed (OFDM) symbols, wherein

the OFDM symbols include a plurality of sub-carrier signals, some of thesub-carrier signals carrying data symbols and some of the sub-carriersignals carrying pilot symbols, the pilot symbols comprising continuouspilot symbols, the continuous pilot symbols being distributed across thesub-carrier signals in accordance with a continuous pilot symbolpattern, the transmitter comprising

a pilot signal former configured to generate pilot symbols,

a symbol builder configured to receive a frequency domain data symbolstream and embed the generated pilot symbols from the pilot signalformer into the sub-carrier signals of the data symbol stream pilotsymbols in accordance with the continuous pilot symbol pattern, and

an OFDM modulator configured to generate a time domain version of thesignal embedded with pilot symbols,

and wherein the pilot signal former comprises a memory configured tostore a master continuous pilot pattern and a processor configured todetect the number of sub-carrier signals in the plurality of sub-carriersignals and to derive the continuous pilot pattern from a master pilotpattern based on the number of sub-carrier signals.

Various further aspects and features of the present disclosure aredefined in the appended claims. Various combinations of features may bemade of the features and method steps defined in the dependent claimsother than the specific combinations set out in the attached claimdependency. Thus the claim dependencies should not be taken as limiting.

It will be appreciated that the above description for clarity hasdescribed embodiments with reference to different functional units,circuitry and/or processors. However, it will be apparent that anysuitable distribution of functionality between different functionalunits, circuitry and/or processors may be used without detracting fromthe embodiments.

Described embodiments may be implemented in any suitable form includinghardware, software, firmware or any combination of these. Describedembodiments may optionally be implemented at least partly as computersoftware running on one or more data processors and/or digital signalprocessors. The elements and components of any embodiment may bephysically, functionally and logically implemented in any suitable way.Indeed the functionality may be implemented in a single unit, in aplurality of units or as part of other functional units. As such, thedisclosed embodiments may be implemented in a single unit or may bephysically and functionally distributed between different units,circuitry and/or processors.

The invention claimed is:
 1. A receiver configured to recovering data from Orthogonal Frequency Division Multiplexed (OFDM) symbols, wherein the OFDM symbols include a plurality of sub-carrier signals, some of the sub-carrier signals carrying data symbols and some of the sub-carrier signals carrying pilot symbols, the pilot symbols comprising continuous pilot symbols, the continuous pilot symbols being distributed across the sub-carrier signals in accordance with a continuous pilot symbol pattern, the receiver comprising: a demodulator configured to detect a signal representing the OFDM symbols, and to generate a sampled digital version of the OFDM symbols in a time domain, a Fourier transform processor configured to receive the time domain digital version of the OFDM symbols and to form a frequency domain version of the OFDM symbols, from which the pilot symbol bearing sub-carriers and the data symbol bearing sub-carriers can be recovered, and a detector configured to recover the data symbols from the data bearing sub-carrier signals of the OFDM symbols and to recover the pilot symbols from the pilot bearing sub-carrier signals of the OFDM symbols, wherein the detector comprises a memory configured to store data relating to a pilot pattern and a processor configured to detect a number of sub-carrier signals in the plurality of sub-carrier signals and to derive the continuous pilot pattern from the pilot pattern data based on the number of sub-carrier signals, and the OFDM symbols comprise first OFDM symbols, which include a first number of sub-carriers signals, and second OFDM symbols, which include a second number of sub-carrier signals, the second number of second sub-carrier signals being the same or greater than the first number of sub-carrier signals, wherein the continuous pilot symbols are present at identical sub-carrier locations in the first OFDM symbols and the second OFDM symbols.
 2. The receiver as claimed in claim 1, wherein the number of sub-carrier signals in the plurality of sub-carrier signals is one of a set of sub-carrier signal numbers and the pilot pattern data represents the pilot symbol pattern for the continuous pilot symbols for OFDM symbols which include a highest number of sub-carrier signals from the set of sub-carrier signal numbers.
 3. The receiver as claimed in claim 2, wherein the set of sub-carrier numbers includes approximately 8 k, 16 k, and 32 k sub-carrier signals, a continuous pilot pattern being provided for the 32 k sub-carrier signals, and the continuous pilot pattern for the 8 k and 16 k sub-carrier signals being derived from the continuous pilot pattern for the 32 k sub-carrier.
 4. The receiver as claimed in claim 3, wherein the continuous pilot symbol pattern for 8 k sub-carriers in terms of sub-carrier signal locations is given by 41, 173, 357, 505, 645, 805, 941, 1098, 1225, 1397, 1514, 1669, 1822, 1961, 2119, 2245, 2423, 2587, 2709, 2861, 3026, 3189, 3318, 3510, 3683, 3861, 4045, 4163, 4297, 4457, 4598, 4769, 4942, 5113, 5289, 5413, 5585, 5755, 5873, 6045, 6207, 6379, 6525, 6675,
 6862. 5. The receiver as claimed in claim 3, wherein the continuous pilot symbol pattern for 16 k sub-carrier signals in terms of sub-carrier signal locations is given by 82, 243, 346, 517, 714, 861, 1010, 1157, 1290, 1429, 1610, 1753, 1881, 2061, 2197, 2301, 2450, 2647, 2794, 2899, 3027, 3159, 3338, 3497, 3645, 3793, 3923, 4059, 4239, 4409, 4490, 4647, 4847, 5013, 5175, 5277, 5419, 5577, 5723, 5895, 6051, 6222, 6378, 6497, 6637, 6818, 7021, 7201, 7366, 7525, 7721, 7895, 8090, 8199, 8325, 8449, 8593, 8743, 8915, 9055, 9197, 9367, 9539, 9723, 9885, 10058, 10226, 10391, 10578, 10703, 10825, 10959, 11169, 11326, 11510, 11629, 11747, 11941, 12089, 12243, 12414, 12598, 12758, 12881, 13050, 13195, 13349, 13517, 13725,
 13821. 6. The receiver as claimed in claim 3, wherein the continuous pilot symbol pattern for 32 k sub-carrier signals in terms of sub-carrier signal locations is given by 163, 290, 486, 605, 691, 858, 1033, 1187, 1427, 1582, 1721, 1881, 2019, 2217, 2314, 2425, 2579, 2709, 2857, 3009, 3219, 3399, 3506, 3621, 3762, 3997, 4122, 4257, 4393, 4539, 4601, 4786, 4899, 5095, 5293, 5378, 5587, 5693, 5797, 5937, 6054, 6139, 6317, 6501, 6675, 6807, 6994, 7163, 7289, 7467, 7586, 7689, 7845, 8011, 8117, 8337, 8477, 8665, 8817, 8893, 8979, 9177, 9293, 9539, 9693, 9885, 10026, 10151, 10349, 10471, 10553, 10646, 10837, 10977, 11153, 11325, 11445, 11605, 11789, 11939, 12102, 12253, 12443, 12557, 12755, 12866, 12993, 13150, 13273, 13445, 13635, 13846, 14041, 14225, 14402, 14571, 14731, 14917, 15050, 15209, 15442, 15622, 15790, 15953, 16179, 16239, 16397, 16533, 16650, 16750, 16897, 17045, 17186, 17351, 17485, 17637, 17829, 17939, 18109, 18246, 18393, 18566, 18733, 18901, 19077, 19253, 19445, 19589, 19769, 19989, 20115, 20275, 20451, 20675, 20781, 20989, 21155, 21279, 21405, 21537, 21650, 21789, 21917, 22133, 22338, 22489, 22651, 22823, 23019, 23205, 23258, 23361, 23493, 23685, 23881, 24007, 24178, 24317, 24486, 24689, 24827, 25061, 25195, 25331, 25515, 25649, 25761, 25894, 26099, 26246, 26390, 26569, 26698, 26910, 27033, 27241, 27449, 27511, 27642,
 27801. 7. The receiver as claimed in claim 6, wherein the number of sub-carrier signals is approximately 16 k and the processor is configured to derive the 16 k continuous pilot pattern according to the equation CP_(—)16K_pos=round(CP_(—)32K_pos(1:2:last_(—)32k_cp_pos)/2).
 8. The receiver as claim in claim 6, wherein the number of sub-carrier signals is approximately 8 k and the processor is configured to derive the 8 k continuous pilot pattern according to the equation CP_(—8)K_pos=round(CP_(—)32K_pos(1:4:last_(—)32k_cp_pos)/4).
 9. The receiver as claimed in claim 1, wherein some of the sub-carrier signals carry scattered pilot symbols distributed across the sub carrier signals in accordance with at least one of a plurality of scattered pilot patterns which include scattered pilot patterns: Dx=4, Dy=4; Dx=8, Dy=2; Dx=16, Dy=2; and Dx=32, Dy=2; and wherein the detector is further configured to recover the pilot symbols from the pilot bearing sub-carrier signals of the OFDM symbols in accordance with the scattered pilot symbol pattern.
 10. The receiver as claimed in claim 1, wherein some of the sub-carrier signals carry scattered pilot symbols distributed across the sub carrier signals in accordance with at least one of a plurality of scattered pilot patterns and in which locations of the scattered pilots across the plurality of scattered pilot symbol patterns and locations of the continuous pilots with respect to the sub-carrier signals substantially do not coincide; and wherein the detector is further configured to recover the pilot symbols from the pilot bearing sub-carrier signals of the OFDM symbols in accordance with the scattered pilot symbol pattern.
 11. A method for receiving and recovering data from Orthogonal Frequency Division Multiplexed (OFDM) symbols, wherein the OFDM symbols include a plurality of sub-carrier signals, some of the sub-carrier signals carrying data symbols and some of the sub-carrier signals carrying pilot symbols, the pilot symbols including continuous pilot symbols, the continuous pilot symbols being distributed across the sub-carrier signals in accordance with a continuous pilot symbol pattern, the method comprising detecting a signal representing the OFDM symbols; generating a sampled digital version of the OFDM symbols in a time domain; receiving the time domain digital version of the OFDM symbols and forming a frequency domain version of the OFDM symbols, from which the pilot symbol bearing sub-carrier signals and the data symbol bearing sub-carrier signals can be recovered; recovering the data symbols from the data bearing sub-carrier signals of the OFDM symbols; and recovering by circuitry the pilot symbols from the pilot bearing sub-carrier signals of the OFDM symbols, wherein the method comprises detecting a number of sub-carrier signals in the plurality of sub-carrier signals; and deriving the continuous pilot pattern from stored data relating to a pilot pattern based on the number of sub-carrier signals.
 12. A transmitter for transmitting Orthogonal Frequency Division Multiplexed (OFDM) symbols, wherein the OFDM symbols include a plurality of sub-carrier signals, some of the sub-carrier signals carrying data symbols and some of the sub-carrier signals carrying pilot symbols, the pilot symbols comprising continuous pilot symbols, the continuous pilot symbols being distributed across the sub-carrier signals in accordance with a continuous pilot symbol pattern, the transmitter comprising a pilot signal former configured to generate pilot symbols, a symbol builder configured to receive a frequency domain data symbol stream and embed the generated pilot symbols from the pilot signal former into the sub-carrier signals of the data symbol stream pilot symbols in accordance the continuous pilot symbol pattern, and an OFDM modulator configured to generate a time domain version of the signal embedded with pilot symbols, and wherein the pilot signal former comprises a memory configured to store data relating to one or more continuous pilots patterns pilot pattern and a processor configured to detect a number of sub-carrier signals in the plurality of sub-carrier signals and to determine the continuous pilot pattern from the pilot pattern data based on the number of sub-carrier signals, and the transmitter is configured to transmit the OFDM symbols, the OFDM symbols comprising first OFDM symbols, which include a first number of sub-carriers signals, and second OFDM symbols, which include a second number of sub-carrier signals, the second number of second sub-carrier signals being the same or greater than the first number of sub-carrier signals, and the continuous pilot symbols are present at identical sub-carrier locations in said first OFDM symbols and the second OFDM symbols.
 13. The transmitter as claimed in claim 12, wherein the number of sub-carrier signals in the plurality of sub-carrier signals is one of a set of sub-carrier signal numbers and the pilot pattern data is the pilot symbol pattern for the continuous pilot symbols for OFDM symbols which include a highest number of sub-carrier signals from the set of sub-carrier signal numbers.
 14. The transmitter as claimed in claim 12, wherein the set of sub-carrier numbers includes approximately 8 k, 16 k, and 32 k sub-carrier signals, the pilot pattern data being provided for the 32 k sub-carrier signals, and the continuous pilot pattern for the 8 k and 16 k sub-carrier signals being derived from the continuous pilot pattern for the 32 k sub-carrier.
 15. The transmitter as claimed in claim 12, wherein the continuous pilot symbol pattern for 32 k sub-carrier signals in terms of sub-carrier signal locations is given by 163, 290, 486, 605, 691, 858, 1033, 1187, 1427, 1582, 1721, 1881, 2019, 2217, 2314, 2425, 2579, 2709, 2857, 3009, 3219, 3399, 3506, 3621, 3762, 3997, 4122, 4257, 4393, 4539, 4601, 4786, 4899, 5095, 5293, 5378, 5587, 5693, 5797, 5937, 6054, 6139, 6317, 6501, 6675, 6807, 6994, 7163, 7289, 7467, 7586, 7689, 7845, 8011, 8117, 8337, 8477, 8665, 8817, 8893, 8979, 9177, 9293, 9539, 9693, 9885, 10026, 10151, 10349, 10471, 10553, 10646, 10837, 10977, 11153, 11325, 11445, 11605, 11789, 11939, 12102, 12253, 12443, 12557, 12755, 12866, 12993, 13150, 13273, 13445, 13635, 13846, 14041, 14225, 14402, 14571, 14731, 14917, 15050, 15209, 15442, 15622, 15790, 15953, 16179, 16239, 16397, 16533, 16650, 16750, 16897, 17045, 17186, 17351, 17485, 17637, 17829, 17939, 18109, 18246, 18393, 18566, 18733, 18901, 19077, 19253, 19445, 19589, 19769, 19989, 20115, 20275, 20451, 20675, 20781, 20989, 21155, 21279, 21405, 21537, 21650, 21789, 21917, 22133, 22338, 22489, 22651, 22823, 23019, 23205, 23258, 23361, 23493, 23685, 23881, 24007, 24178, 24317, 24486, 24689, 24827, 25061, 25195, 25331, 25515, 25649, 25761, 25894, 26099, 26246, 26390, 26569, 26698, 26910, 27033, 27241, 27449, 27511, 27642,
 27801. 16. A method for transmitting Orthogonal Frequency Division Multiplexed (OFDM) symbols, wherein the OFDM symbols include a plurality of sub-carrier signals, some of the sub-carrier signals carrying data symbols and some of the sub-carrier signals carrying pilot symbols, the pilot symbols comprising continuous pilot symbols, the continuous pilot symbols being distributed across the sub-carrier signals in accordance with a continuous pilot symbol pattern, the method comprising generating pilot symbols; receiving a frequency domain data symbol stream and embedding the generated pilot symbols into the sub-carrier signals of the data symbol stream in accordance with a scattered pilot symbol pattern and the continuous pilot symbol pattern; and generating by circuitry a time domain version of the symbol stream embedded with the pilot symbols, and the method comprises detecting a number of sub-carrier signals in the plurality of sub-carrier signals; and deriving the continuous pilot pattern from stored data relating to a pilot pattern based on the number of sub-carrier signals, wherein the OFDM symbols comprise first OFDM symbols, which include a first number of sub-carriers signals, and second OFDM symbols, which include a second number of sub-carrier signals, the second number of second sub-carrier signals being the same or greater than the first number of sub-carrier signals, and the continuous pilot symbols being present at identical sub-carrier locations in the first OFDM symbols and the second OFDM symbols.
 17. A non-transitory computer readable medium including computer program instructions, which when executed by a computer causes the computer to perform the method according to claim
 16. 